Bilateral coaxial resistive device having coaxial and coextensive resistor elements



March 28, 1967 CONNEY BILATERAL COAXIAL RESISTIVE DEVIQE HAVING COAXIAL AND COEXTENSIVE RESISTOR ELEMENTS Filed April 15, 1965 2 Sheets-Sheet 1 FIGI.IA

FIG.|B

BY 144m March 28, 1967 M. CONNEY 3,311,856

BILATERAL COAXIAL RESISTIVE DEVICE HAVING GOAXIAL AND COEXTENSIVE RESISTOR ELEMENTS Filed April 15, 1965 2 Sheets-Sheet 2 l/VPUI' OUTPUT FIG.2C

INVENTOR. M09554; 4/: CON/V5) United States l atent Ofiiice 3,312 L855 Patented Mar. 28, 1967 3,311,856 BILATERAL CUAXKAL RESEIS'HVE DEVKIE HAV- liNG CQAXEAL AND COIEXTENSWE RESISTQR ELEMENTS Marcellus Cortney, 13 McDonnell St., Amsterdam, NY. 12010 Filed Apr. 15, 1965, Ser. No. 448,431 Claims. (Cl. 333-311) This invention relates to coaxial devices. More particularly, it relates to improved bilateral resistive coaxial devices which enable advantageous bilateral impedance matching over substantially the entire coaxially-usable frequency spectrum.

Heretofore, a basic problem encountered in known resistive coaxial devices intended for covering a wide frequency range (.D.C. to 11 -kmc., for example) or significant portions of such range has been the inherent discrepancy presented between the lumped aspects of the shunt resistive elements which have been utilized in the device and the distributed aspects of the coaxial structure itself. Although prior art structures have enabled the matching of these aspects in a unilateral device, it has not been able to accomplish the matching of these aspects bilaterally.

As is well known, in presently used coaxial devices, shunt resistive elements appear as a lumped resistance at all frequencies whereas series resistive elements normally appear distributed since they lie along the center con ductor of a coaxial line. At D.C., both the series and shunt resistive elements, of course, appear lumped. However, as frequency increases toward the microwave region, the shunt resistive elements remain lumped but the series resistive elements increasingly become a distributed impedance. Of necessity, therefore, the relationship between the series and shunt elements changes as a function of frequency thereby making it impracticable to optimize performance of the device over the entire coaxially usable spectrum.

It is accordingly an important object of this invention to provide a coaxial device in which the coaxial relationship of the shunt resistive elements with the series resistive elements and the surrounding structure is maintained substantially coaxially constant with frequency.

It is another object to provide a coaxial device in accordance with the preceding object which enables bilateral impedance matching over substantially the whole coaxially-usable spectrum.

Generally speaking, the basic concept of the invention is to make the shunt resistive element appear distributed while maintaining a coaxial relationship with the series element, such relationship remaining constant with frequency. Accordingly, there is provided a coaxial device comprising a structure adapted to be inserted into electrical circuit in alignment with a conductor, the structure including first resistance means disposed in the aforesaid alignment and second resistance means coaxially disposed with the first resistance means and having its midpoint in electrical contact with the first resistance means.

For a better understanding of the invention together with other and further objects thereof, reference is had to the following description taken in conjunction with the accompanying drawing and its scope is pointed out in the appended claims.

In the drawings:

FIG. 1A is a side elevation, partly in section, of the known bilateral coaxial device inserted in circuit with a coaxial cable;

FIG. 1B is a side elevation, partly in section, of a unilateral coaxial device inserted in circuit with a coaxial cable;

FIG. 1C is a schematic diagram of the electrical circuit provided by the device of FIG. 1A;

FIG. 2A is a side elevation partly in section of an illustrative embodiment of a bilateral coaxial device constructed in accordance with the principles of the invention inserted in circuit with a coaxial cable;

FIG. 2B is an exploded three dimensional view of the resistive elements included in the device shown in FIG. 2A; and

FIG. 2C is a schematic diagram of the electrical circuit provided by the device of FIG. 2A.

Referring now to FIG. 1A wherein there is shown a presently known bilateral coaxial device It), the series resistive elements comprise a pair of rods 12 and 14 dis posed on the coaxial line of the central conductor 16 which makes electrical contact with device It at an input end 18 and an output end 20, resistive rod elements 12 and 14- being electrically connected by a coaxially aligned conductive member 22. Also making electrical connection with member 22 and outer conductor 24 is the shunt resistive element 26 which is shown as physically comprising a disc, suitably composed of a dielectric material such as ceramic coated with a resistive material such as carbon. A pair of conductive sleeves 28 and 3!) of roughly truncated conical configuration are coaxially disposed With resistive elements 12 and 14 and are chosen, in accordance with known procedures, to have diameters and tapers for providing desired input characteristic impedances. The smaller diameter ends of sleeves 23 and 30 terminate in flanges which make contact with disc 26. The remaining structures of the device of FIG. 1A are the ones usually found in coaxial devices such as the insulation 32 enveloping inner conductor 16 and the outer conductor 24 functioning as a shield, etc.

in FIG. 1B, there is shown a unilateral device In this device, since its structure is quite similar to the structure of FIG. 1A, elements corresponding to like elements therein in the structure of FIG. 1A have been given the same numerical designation but with the prime notation. It is seen that the essential difference between the devices of FIGS. 1A and 1B is the shape and disposition of the truncated conical structure 36, i.e., it is larger and its smaller diameter end is located at the output end of the device.

In FIG. 10 wherein there is shown an electrical diagram corresponding to the structure shown in FIG. 1A, resistances R and R are provided by series resistive rod elements 12 and 14 respectively and shunt resistance R is provided by disc 26. Conductor 4G is provided by truncated conical structures 28 and 30.

Considering the operation of the device of FIG. 1A in conjunction with the schematic diagram of FIG. 1C, under direct current conditions, resistances R R and R are, of course, all lumped. However, as frequency increases, particularly as it moves progressively into the UHF and microwave regions, series resistances R and R become increasingly distributed impedances while shunt resistance R remains lumped. Consequently, the relationship between the series resistances and shunt resistance necessarily changes as a function of frequency. Because of this phenomenon, optimization of performance of the device over the entirely coaxially usable spectrum canot be practicably accomplished.

To illustrate the above deficiency, let it be assumed that the device of FIG. 1A is intended to be used as an attenuator pad which provides an attenuation of 10 db and with desired input and output impedances at ends 18 and 2% to be 50 ohms. In such situation, with resistances R and R chosen to have a value of 25.94 ohms and resistance R to have a value of 35.14 ohms, the required characteristic impedance at point all is equal to 24.06

a 3 ohms. The impedance Z at point 42 ideally should be equal to 75.94 ohms. However in the structure of FIG. 1A for it to function bilaterally the characteristic impedance of the structure at point 42 is required to be 24.06 ohms.

In the unilateral construction shown in FIG. 1C, there is enabled a very good voltage standing wave ratio and input impedance matching at end 18'. However, the matching at output end 26' is poor. With the same values as chosen hereinabove for the elements of the structure of FIG. 1A, i.e., 25.94 ohms for resistive elements R and R and 35.14 ohms for resistive elements R Z at point 42 in FIG. 1C is 75.94 ohms, as is required by the resistor values for input matching.

In FIG. 2A wherein there is shown a coaxial attenuator T pad 45 constructed in accordance with the principles of the invention, the series resistive elements comprise a pair of rod resistive elements 46 and 48 respectively. The shunt resistive element comprises a pair of truncated conical resistive elements 50 and 52 disposed coaxially with series resistive elements 46 and 48 respectively. The ratio of the respective diameters of the larger ends of conical resistive elements 50 and 52 and the diameters of rods 46 and 48 are chosen to provide the desired input characteristic impedance Which typically may be 50 ohms. The physical length of conical resistive elements 50 and 52 are chosen to be approximately the same as rod resistive elements 46 and 48, the smaller diameter ends of conical resistive elements 50 and 52 making a close fit and electrical connection with rod resistive elements 46 and 48. It is seen that resistive elements 46 and 48 and resistive elements 50 and 52 together form a distributed coaxial device. A sleeve resistive element 54, tapered longitudinally from both ends toward its center is coaxially disposed around truncated conical resistive elements 50 and 52 and is chosen to have a zero ohms characteristic input impedance Z at input points 56 and a characteristic impedance at output point 58 as determined by the resistance values. The remaining structures in the device of FIG. 2A are the usual structures in the attenuator pads such as the outer conductor 60. The inner conductor 62 enveloped by an insulating layer 64 suitably makes electrical connection with the device at its input and output ends 66 and 68 respectively.

In considering the operation of the device shown in FIG. 2A, reference is made to the electrical schematic diagram corresponding thereto as shown in FIG. 2C. In this diagram, series resistances R and R correspond to resistive elements 46 and 48 and shunt resistances R and R correspond to truncated conical resistive elements 50 and 52. In this diagram, in a particular design application such as a db attenuator, resistances R and R may be chosen to each have a value of 25.97 ohms. Resistances R and R may be chosen to each have a value of 70.28 ohms. Sleeve 54 is designated in FIG. 2C as conductor 54. With this arrangement, the input impedance, Z is 50 ohms. The impedance Z at points 56 is 0 ohms, the impedance, Z at points 57 is 0 ohms, and the impedance Z at points 58 is 36.5 ohms. The output impedance Z, at points 68 is 50 ohms.

From the foregoing, it may be readily understood that a single coaxial cone-rod structure consisting of the elements to the left of the center line of FIG. 2A provides a resistive impedance transformation from a given input impedance, such as 50 ohms to some lower impedance value as determined both by the values of the resistances and the coaxial structure. The impedance of the coaxial structure and the required impedance as determined by the resistance values are closely matched along the conerod resistance combination and, therefore, substantially no discontinuities exist. Consequently, the impedance transformation essentially is capable of satisfactorily covering the entire coaxial-frequency spectrum and is completely bilateral over the frequency range of such spectrum. A T type attenuator pad with 50 ohms input and output impedance would comprise two of the aforesaid impedance transformations and would be disposed in back to back relationship as shown in FIG. 2A. In this type of device, because the impedance elements are matched along substantially the entire length of the resistive elements, the frequency response thereof is rendered independent of physical length and consequently such device enables the construction therefrom of broad band attenuator units having a high power dissipation rating and excellent voltage standing wave ratio and insertion loss characteristics.

It should be further understood that if a coaxial transmission line of the required impedance is substituted for the cone-rod structure to the right of the center line in FIG. 2A, with the center conductor of the transmission line connected to resistor 46 at point 58, and the outer conductor of the. transmission line connected to the outer conductor of the structure of point 58, and if the other end of this transmission line is connected to the output circuit, such a configuration would operate as a resistive impedance transformer. Using the same resistor values as given previously for the 10 db attenuator pad, wherein rod resistor 46 has the value of 25.97 ohms, and conical resistor 50 has the value of 35.14 ohms, the input impedance of the device would be 50 ohms, and the output impedance would be 25.06 ohms.

It is apparent that exchanging the input and output connections to the device as described yields a broadband resistive transformer capable of matching a relatively low input impedance (24.06 ohms) to a relatively high output impedance (50 ohms), it being understood that the exact transformation values are a function of the values selected for rod resist-or 46 and conical resistor 50, corresponding appropriate changes being made in the dimensions of the coaxial structure to match the input and output impedances thus achieved.

FIG. 2B shows in three-dimensional exploded depiction, the rod resistive elements 46 and 48 and truncated conical resistance elements 50 and 52 of FIG. 2A. In the making of the structure of FIGS. 2A and 2B, rod resistive elements 46 and 48 may suitably be insulating forms of a dielectric material such as ceramic having thin resistive films deposited thereon in a suitable manner well known in the art. Resistive truncated conical elements 56 and 52 may suitably be insulating forms of a dielectric material such as ceramic and may have the resistive films deposited on both their inner and outer surfaces. Areas 47 and 49, and 51 and 53 on resistive elements 46 and 48 and areas 55 and 57, and 59 and 61 on truncated conical resistive elements 50 and 52 may be suitably of silver or coated with silver to provide electrical contact areas.

While there have been described what are considered to be the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed as new and desired to be secured by Letters Patent of the US. is:

1. A coaxial device comprising a structure adapted to be inserted into electrical circuit in alignment with a conductor, said structure including first resistance means disposed in said alignment and second resistance means coaxially disposed both with said first resistance means along a portion of the length of said first resistance means and with surrounding coaxial structure to provide a device having chosen characteristic impedances at each point along the length of said device.

2. A coaxial device comprising a structure adapted to be inserted into electrical circuit in alignment with a conductor, said structure including first of rod shaped resistive means disposed in said alignment, and second truncated conical resistive means coaxially disposed with said first resistive means respectively, said first and second resistive means being in electrical contact at a common junction point.

3. A coaxial device comprising a structure adapted to be inserted into electrical circuit in alignment with a conductor, said structure including a first pair of rod shaped resistive elements disposed in said alignment and a second pair of truncated conical resistive elements coaxially disposed with each of said first pair of resistive elements respectively, all of said resistive elements being in electrical contact at a common junction point.

4. A coaxial device comprising a structure adapted to be inserted into electrical circuit in alignment with a conductor, said structure including a first pair of rod shaped resistive elements disposed in said alignment, and a second pair of truncated conical resistive elements having the same axial length respectively as each of said first resistive elements and coaxially disposed therewith, said second resistive elements being disposed in opposing relationship at their lesser diameter ends, said lesser diameter ends of said second resistive elements and the opposing ends of said first resistive elements all being in electrical contact at a common junction point.

5. A coaxial device comprising a structure adapted to be inserted into electrical circuit in alignment with a conductor, said structure including a first pair of rod shaped resistive elements disposed in said alignment, and a second pair of truncated conical resistive elements having the same length respectively as each of said first resistive elements and coaxially disposed therewith, said second resistive elements being disposed in opposing relationship at their lesser diameter ends, the greater diameters of said second resistive elements being respectively so chosen as to provide a ratio with the diameters of said rods to provide a given input impedance characteristic for said structure, said lesser diameter ends of said second resistive elements and the opposing ends of said first resistive elements all being in electrical contact at a common junction point.

6. A coaxial device comprising a structure adapted to be inserted into electrical circuit in alignment with a conductor, said structure including a first pair of rod shaped resistive elements disposed in said alignment, a second pair of truncated conical resistive elements having the same length respectively as each of said first resistive elements and coaxially disposed therewith, said second resistive elements being disposed in opposing relationship at their lesser diameter ends, the greater diameters of said second resistive elements being respectively so chosen as to provide a ratio with the diameters of said rods to provide a given input impedance characteristic for said structure, said lesser diameter ends of said second resistive elements and the opposing ends of said first resistive elements all being in electrical contact at a common junction point, and a sleeve disposed in coaxial relationship with said second resistive elements and in electrical contact therewith at said greater diameter ends.

7. A coaxial device comprising a structure adapted to be inserted into electrical circuit in alignment with a conductor, said structure including a first pair of rod shaped resistive elements disposed in said alignment, a second pair of truncated conical resistive elements having the same length respectively as each of said first resistive elements and coaxially disposed therewith, said second resistive elements being disposed in opposing relationship at their lesser diameter ends, the greater diameters of said second resistive elements being respectively so chosen as to provide a ratio with the diameters of said rods to provide a given input impedance characteristic for said structure, said lesser diameter ends of said second resistive elements and the opposing ends of said first resistive elements all being in electrical contact at a common junction point, and a sleeve tapered from its ends to its midpoint disposed in coaxial relationship with said second resistive elements and in electric-a1 contact at its ends with said greater diameter ends of said second resistive elements, the junction of one sleeve end and the greater diameter of one of said second resistive elements having a characteristic input impedance of zero ohms, the junction of the other end of said sleeve and the greater diameter end of said other second resistive element having a characteristic output impedance in accordance with the resistance values of said resistive elements.

8. A coaxial device as defined in claim 7 wherein each of said first resistive elements comprise a rod shaped member of dielectric material having a resistance film thereon, and end portions of electrical conductive material and wherein each of said second resistive elements comprises a hollow-truncated conical member of dielectric material having said resistance film thereon on one of its surfaces and end portions of electrically conductive material.

9. A coaxial device as defined in claim 7 wherein each of said first resistive elements comprise a rod shaped member of dielectric material having a resistance film thereon, and end portions of electrically conductive material and wherein each of said second resistive elements comprises a hollow-truncated conical member of dielectric material having said resistance film thereon on both of its surfaces and end portions of electrically conductive material.

10. A coaxial device comprising a structure adapted to be inserted into electrical circuit in alignment with a conductor, said structure including a first resistive element disposed in said alignment, and a second truncated conical resistive element having the same axial length as said first resistive element coaxially disposed therewith, a coaxial structure having a given characteristic impedance for connecting the smalled diameter end of said second resistive element to said conductor to provide said coaxial device having a lower characteristic at said smaller diameter end whereby said last named device is capable of operating as a resistive impedance transformer over a wide frequency range.

References Cited by the Examiner UNITED STATES PATENTS 2,620,396 12/1952 Johnson et a1 333-81 2,700,733 1/1955 Brueckmann 343-733 2,831,163 4/1958 Stevens 333-81 2,968,774 1/1961 Rodriguez 333-81 3,176,250 3/1965 Marchaud et al 333-81 HERMAN KARL SAALBACH, Primary Examiner. R. F. HUNT, Assistant Examiner. 

1. A COAXIAL DEVICE COMPRISING A STRUCTURE ADAPTED TO BE INSERTED INTO ELECTRICAL CIRCUIT IN ALIGNMENT WITH A CONDUCTOR, SAID STRUCTURE INCLUDING FIRST RESISTANCE MEANS DISPOSED IN SAID ALIGNMENT AND SECOND RESISTANCE MEANS COAXIALLY DISPOSED BOTH WITH SAID FIRST RESISTANCE MEANS ALONG A PORTION OF THE LENGTH OF SAID FIRST RESISTANCE MEANS AND WITH SURROUNDING COAXIAL STRUCTURE TO PROVIDE A DEVICE HAVING CHOSEN CHARACTERISTIC IMPEDANCES AT EACH POINT ALONG THE LENGTH OF SAID DEVICE. 